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18 Dec 2019

The bleach we used in our lab experiment "Kinetics of Bleach" has 6% NaOCl.

One of our post lab questions is "Calculate the concentration of the bleach that was used in today's experiment. The % NaOCl is written on the mottle (%m/v)." How do I calculate the concentration of bleach?

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Lelia Lubowitz
Lelia LubowitzLv2
31 Dec 2019

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Related questions

Equipment Materials

50.00 ml buret, 250.ml volumetric flask, 1.00 ml volumetric pipet 10.0 mL volumetric pipet, 25.00 mL volumetric pipet, pipettor, 250 mL Erlenmeyer flask, 10.0 mL graduated cylinder, several beakers, several watchglasses, unkown bleach solution, 10% potassium iodide solution, 2M hydrochloric acid solution, 0.150 M sodium thiosulfate solution, 1% starch solution.

Background information regarding this experiment is as follows:

An aqueous solution of sodium hypochlorite (NaOCI) is a clear, slightly yellow liquid, and is commonly known as bleach. Aside from its uses as a bleaching agent, sodium hypochlorite solutions are also used as sterlizing agents and in water treatment. Industrial uses include agricultural, food handling, paper production, and textile production. Sodium hypochlorite is also added to waste water to reduce odors.

The concentration of sodium hypochlorite in bleach solutions can be determined by titration. Therefore, we must use a two-step method to titrate sodium hypochlorite. In the first step, sodium hypochlortie, hydrochloric acid, iodide ion, and starch are combined to form a starch-triiodide complex. In this step there are 3 reactions that take place:

The result of these 3 reactions is that when sodium hypochlorite is present the starch-triiodide complex is produced.

In the second step the starch-triiodide product is titrated by sodium thiosulfate to form a colorless solution of iodide, dithionate.

I do not know how to answer the following on the data sheet: (? means I do not know how to answer)

Table 1:

Mass of 1.00 ml of unknown (by tare): 10.552 g

Density of bleach: (g/ml) : 1.055 g/ml

Volume of diluted bleach used in each titration: 10.00

Concentration of sodium thiosulfate: ? (M)

Titration Data:

Initial buret reading (ml): trial1: 0.000 ml Trial 2: 0.00 ml Trial 3: 0.000ml

Final buret reading (ml): trial 1: 13.50ml Trial 2: 13.30ml Trial 3: 13.40ml

Volume delivered(ml: trial 1: ? Trial 2: ? trial 3:?

Calculations: (show clearly)

For trial 1,2,3 ???

1.Moles of Na2S2O3 in titration: ??? trial 1,2,3

2.Moles of NaOCl: ???trial 1, 2,3

3.Average moles of diluted NaOCl: (one answer) ?

4.Average moles of undiluted NaOCl: (one answer.. mol) ?

5.Standard Deviation: (one answer) (mol)

6.Average mass of NaOCl in 25.00mL of undiluted bleach: ? (g)

7.mass of 25.00 mL of undiluted bleach: ? (g)

8. Mass % of NaOCL from experiment: ? (%)

9.Actual mass % of NaOCL (from prof; student does not make an entry):? (%)

More questions all need to be answered please:

1. Calculate the volume of the reagent thiosulafte solution which would be required if you titrated a 25ml sample of the original commercial bleach instead of 25ml of the diluted solution.

2. Why would we choose a graduated cylinder to measure the HCl and KI solutions instead of a volumetric pipette? When would we use a volumetric pippette?

3. You calculated the mass percent of sodium hypochlorite in the bleach( dilute and undiluted). Now calculate the molarity of the sodium hypochlorite in the diulte and undiluted solution/

4. Use oxidation states to show that equations (2) and (4) in the introduction are redox reactions and that equation 1 is not a redox reaction. :

-(1) NaOCl(aq) + HCl(aq) yields HOCl(aq)+NaCl(aq)

-(2) HOCL (aq) + HCl(aq) + 3I(aq) yields I3(aq) + 2CL(aq) + H2O(l)

-(4) (I3) (Starch) + 2S2O3 yields 3I + S4O6 + starch

5. combine equation 1-3 to show the overall reaction for the products of the starch-triiodide complex.

-(1) NaOCl(aq) + HCl(aq) yields HOCl(aq)+NaCl(aq)

-(2) HOCL (aq) + HCl(aq) + 3I(aq) yields I3(aq) + 2CL(aq) + H2O(l)

-(3) I3 + Starch yields (I3) (Starch)

6. What standard was used in this experiment?

7. Describe the naming of NaClO and HClO. What are the names of the following compounds? NaClO2 , NaClO3, NaClO4 , HClO2, HClO3, HClO4

8 Submit a one paged (typed double spaced) report that discusses the following topics:

a. the goals or objectives of the experiment

b.your results as they relate to the goals and objectives

c. the quality of your results.

Question:1 (NOTE: liquid bleach refers to the original sample of liquid bleach.; bleach solution refers to the diluted sample of liquid bleach) A 10.0 mL sample of liquid bleach is diluted to 100 mL in a volumetric flask. A 25.0 mL sample of this bleach solution is analyzed according the procedure described in the lab. 21.3 mL of a 0.159 M solution of Na2S2O3 is needed to reach the stoichiometric point of the titration. Calculate the number of moles of ClO- that are present in the 25.0 mL sample of bleach solution.

How many grams of Cl2 are equivalent to the number of moles of ClO- calculated above?

How many grams of liquid bleach are actually analyzed? Assume that the density of liquid bleach is 1.084 g/mL.

Calculate the percent "available chlorine" in the liquid bleach.






Question:2
Balance the following redox equation (a reaction that occurs in this week's lab) using the method discussed in Section 19.1 in your textbook. The reaction occurs in basic solution. Show all your work, including the half-reactions that lead to the final balanced equation and the number of electrons that must be used to balance each half reaction.

ClO-(aq) + I-(aq) รขย†ย’ I2(aq) + Cl-(aq)

1- In the titration between potassium iodate and the sodium thiosulfate solution, if the titration is not performed immediately after the addition of the sulfuric acid, how would this likely affect the calculated concentration of your diluted sodium thiosulfate solution?

2- Why did the titrations performed need to be started immediately after adding the sulfuric acid?

3- A sample of bleach was analyzed as in this procedure. The only procedural difference is that the student weighed out the bleach solution used instead of pipetting a certain volume of bleach. The student weighed out 0.634 g of commercial bleach solution. It was found that it required 13.24 mL od 0.0732 M sodium thiosulfate solution to react with the iodine produced. What is the percentage of sodium hypochlorite in this bleach sample?

4- The active ingredient in many commercial liquid bleaches is sodium hypochlorite. The bottle lists the percentage of sodium hypochlorite as 6.0%. If the density of commercial bleach is 1.084 g/mL of 0.150 M sodium thiosulfate is required to reach the end point in a titration similar to the one performed in this experiment, if a student analyzed a 2.0 mL sample of bleach.

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